Food Web Dynamic Model Development And Stability Analysis In Lake Balihe

Phytoplankton and zooplankton are the most important primary producer and consumer in aquatic ecosystems.The biomass and stability of plankton community are important in maintaining the functioning of freshwater ecosystems.In recent years,eutrophication caused by global climate change and human activities has become more and more serious.Water eutrophication would lead great changes in the structure of ecosystems,including species biomass fluctuations and extinction.In aquatic ecosystem,species generally have interactions with each other.Changes in the biomass of one species often affect other species or even the whole ecosystem.Therefore,it is essential to systematically study the food web structure of aquatic ecosystems,and to study the interaction between species and the stability of biomass changes.In the present study,we select Lake Balihe,a freshwater lake located at Yingshang County,Fuyang City,Anhui province,China.Main environmental factors,the density and biomass of phytoplankton,zooplankton,benthic and fish species were investigated.The predation relationships among fish species and plankton were determined through the investigation and fish stomach content analysis.A food web model was built and the parameters were determined from field investigations and species physiological allometry relationships with body mass.The effects of nutrient concentrations,fish predation on the biomass and temporal stability index(TSI)of plankton were analyzed.As a result,the following can be concluded.(1)In the lake,fish biomass was dominant by Aristichthy's nobilis,Cyprinus carpio,Hypophthalmichthy's molitrix,and Culter erythropterus Basilewsky,and their biomass proportions were 50.76%,13.40%,13.20%,and 9.96%,respectively.There were 129 species in fish stomach content,including 76 phytoplankton species,41 zooplankton species,8 benthic species,and 8 macrophytes species.The biomass of zooplankton and phytoplankton was accounted for 99.4%of total fish stomach content.Species Aristichthy's nobilis,Cyprinus carpio,and Culter erythropterus mainly prey on zooplankton,while the main food of Hypophthalmichthys molitrix was phytoplankton.(2)The results of stable isotope analysis showed that phytoplankton and macrophytes are the first trophic level in the food web of Lake Balihe.Zooplankton and benthos are the second trophic level.H.molitrix and Ctenopharyngodon idellus are the 2nd to 3rd trophic levels.Aristichthys nobilis,Carassius auratus,and Pseudorasbora parva are the third trophic level.Fish species Culter erythropterus are the forth trophic level.(3)The results of food web model showed that appropriate concentrations of nitrogen and phosphorus(nitrogen less than lmg/L,phosphorus less than 0.2mg/L)would promote the biomass of plankton,while excessive nutrients would decrease the growth of plankton.When the concentration of nutrient was low(nitrogen was less than 0.5mg/L,phosphorus was less than 0.1mg/L),the increase of nutrient concentration promoted the TSI of plankton community in the lake.When the concentration of nutrient was high,it would decrease the TSI of biology community in the lake.When the concentration ratio of nitrogen and phosphorus was 5,the biomass of fish increased obviously.There was no obvious correlation between the TSI of Culter erythropterus and nutrient concentration.(4)The increase of H.molitrix would not decrease the biomass of phytoplankton due to the complex species interactions although there was predation relationship between them.An appropriate amount of H.molitrix and A.nobilis would benefit the survival of phytoplankton,H.molitrix and C.erythropterus,while high levels of them would have negative effects.The amount of H.molitrix and A.nobilis can inhibit the survival of zooplankton and C.idellus.Appropriate interaction strength among fishes would benefit the survival of plankton,while high interaction strength would inhibit the growth of plankton.The TSI of phytoplankton is positively correlated with the amount of H.molitrix and A.nobilis.The stability of zooplankton and all fishes has a unimodal relationship with the amount of H.molitrix and A.nobilis.A.nobilis was the winner in the competition of fish predation.The biomass of A.nobilis was increased with the increase of competition intensity.The results in this research will be helpful in understanding the interactions among species in aquatic ecosystems.The methods in modeling the lake ecosystem are also helpful in analyzing natural aquatic ecosystems.